158,341 research outputs found

    A model based framework for air quality indices and population risk evaluation, with an application to the analysis of Scottish air quality data

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    The paper is devoted to the development of a statistical framework for air quality assessment at the country level and for the evaluation of the ambient population exposure and risk with respect to airborne pollutants. The framework is based on a multivariate space–time model and on aggregated indices defined at different levels of aggregation in space and time. The indices are evaluated, uncertainty included, by considering both the model outputs and the information on the population spatial distribution. The framework is applied to the analysis of air quality data for Scotland for 2009 referring to European and Scottish air quality legislation

    A multiple factor model for European stocks

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    We present an empirical study focusing on the estimation of a fundamental multi-factor model for a universe of European stocks. Following the approach of the BARRA model, we have adopted a cross-sectional methodology. The proportion of explained variance ranges from 7.3% to 66.3% in the weekly regressions with a mean of 32.9%. For the individual factors we give the percentage of the weeks when they yielded statistically significant influence on stock returns. The best explanatory power – apart from the dominant country factors – was found among the statistical constructs „success“ and „variability in markets“.Vorgestellt wird eine empirische Studie, welche die Schätzung eines fundamentalen Multi-Faktor-Modells für ein Universum europäischer Aktien beinhaltet. Als Methode wurde in Anlehnung an die Vorgehensweise im BARRA-Modell der Querschnittsanalyse der Vorzug gegeben. Der Anteil der erklärten Varianz beläuft sich in den wöchentlichen Regressionen auf 7,3% bis 66,3% bei einem Durchschnitt von 32,9%. Für die einzelnen Faktoren wird die Häufigkeit angegeben, mit der sie sich in den Regressionen signifikant erwiesen haben. Den höchsten Erklärungsgehalt im Untersuchungszeitraum hatten Länderfaktoren, aber auch Konstrukte wie „Success“ oder „Variability in Markets“

    The internal reliability of some City & Guilds tests

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    Combined MASS-DIMM instrument for atmospheric turbulence studies

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    Several site-testing programs and observatories currently use combined MASS-DIMM instruments for monitoring parameters of optical turbulence. The instrument is described here. After a short recall of the measured quantities and operational principles, the optics and electronics of MASS-DIMM, interfacing to telescopes and detectors, and operation are covered in some detail. Particular attention is given to the correct measurement and control of instrumental parameters to ensure valid and well-calibrated data, to the data quality and filtering. Examples of MASS-DIMM data are given, followed by the list of present and future applications.Comment: Accepted by MNRAS, 11 pages, 8 figure

    Salt marsh harvest mouse abundance and site use in a managed marsh

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    The salt marsh harvest mouse (Reithrodontomys raviventris) is a federal and California listed endangered mammal endemic to the San Francisco Bay. The objectives of this research were to determine habitat use of endangered salt marsh harvest mice in a managed marsh in Fremont California, and to evaluate whether managed flooding of the marsh provides favorable habitat conditions for the mice. In addition, this research explores the effectiveness of using mark-recapture model selection analysis to estimate capture probability, survival, and population growth rate for salt marsh harvest mice. Mice were captured for four nights per month between May and August, 2008. Thirty-six unique salt marsh harvest mice were captured for a catch per 100 nights of trap effort of 1.9. The sex ratio of male to female mice was skewed towards males with a sex of 2.3:1. Salt marsh harvest mice were distributed randomly throughout the marsh and no relationships were found between mice distribution and pickleweed salinity, pickleweed height, distance to levees, distance to dry or filled water bodies, percent cover of vegetation, or sympatric rodents. The findings of this study indicate that catch-per-trap-effort, the current standard method to estimate salt marsh harvest mice populations, may not be accurate. The results of this study can be used by managers of salt marsh harvest mice habitat to manage and estimate mouse populations

    Hedonic Regressions, Matched Models and Economic Theory

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    Quality adjustment of price indexes affects the analysis of many sensitive economic issues, such as real growth, productivity, international competitiveness, real wages, per-capita consumption and poverty, other than inflation. Hedonic methods are often recommended and increasingly used in the compilation of consumer price indexes. Nevertheless many official statistical agencies continue adopting traditional methods considering only the dynamics of prices of products matching in two adjacent periods of time. Indeed, a number of studies have even recently remarked that hedonic methods sometimes provide results very similar to the traditional matching models approach, particularly when models included in price index sample are replenished frequently. This paper briefly surveys the economic theory behind hedonic and traditional quality adjustment methods, and demonstrates that average price changes estimated by hedonic regressions differ from matched models estimation only because of the sum of regression residuals associated to disappearing and new models included in the sample. Thus, hedonic regressions including among the explanatory variables some indicators of the novelty and oldness of models provide exactly the same results of traditional methods. This fact casts some doubt on the overall effectiveness of hedonic methods in quality adjustment. The paper also focuses on that some economic and statistical hypotheses underlying hedonic methods possibly conflict with the assumptions and practices embodied in compiling the harmonised index of consumer prices for European countries.Consumer price index; Harmonised Index of Consumer Prices (HICP); Hedonic regressions; Matched models; Measurement of inflation; Quality adjustment
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